This invention relates to a method for providing edge-side tracks of holes at a printing belt for a rotary printing machine with at least one counter pressure cylinder and at least two printing belt cylinders around which a continuous printing belt carrying printing forms or printing pictures is led, with at least one such cylinder being provided with a radial ring of pins in the region of each of its ends, wherein pins mesh with holes of the edge-side tracks of holes of the printing belt for slip-free guiding of the belt, and also relates to an apparatus for carrying out said method.
Rotary printing machines of said kinds which are provided with continuous printing belts, by which the format length can be increased independent of the diameters of the printing belt cylinders, which form idler rollers, are known for instance from the German Utility Model G 81 22 637.3 and the German Patent 444,987.
For the preparation of a print, printing belt sections, which can e.g. be belts made of polyester film, at their side edges are provided with the tracks of holes by punching. The printing belt is then put around the printing belt cylinders such that the holes of the edge-side tracks of holes mesh with the pins of the radial rings of pins of the printing cylinder. The ends of the printing belt section are connected with each other so that the continuous printing belt is obtained. For the connection of the ends of a printing belt section they can be provided with tooth rows being undercut in a dovetailed form, which can be brought into a positive engagement with each other. The engagement of the two tooth rows can then be secured by adhesive tapes glued thereto. The printing belts carry in a usual manner the blocks which can be glued thereto.
The continuous printing belt being led in a printing machine over the printing belt cylinders is subject to a certain tension so that it is elastically stretched. Said elastic stretching has the effect that the circular holes of the edge-side perforations, punched in the slack printing belt, are ovally or elliptically deformed in longitudinal direction of the printing belt, so that between the pins of the pin rings and the holes of the edge-side perforations a backlash is obtained and a slip-free guidance of the printing belt on the printing belt cylinder is no longer guaranteed. Said backlash resulting from the elliptical deformation of the holes can lead to a blurring of the printing image. Moreover, due to a stretching of the printing belt, the spacing of the holes of the edge-side perforations no longer corresponds to the spacing of the pins of the radial pin rings so that troubles can also occur in this respect.